Currently, separation technology is broadly used in various chemical processes for obtaining high purity chemical products, increasing the conversion of the desired compounds or products in the chemical processes, and decreasing the production cost, and has been improved continuously.
In general, the known separation processes include a colloidal filtration process, an ion exchange process and an affinity chromatographic process, wherein the separation is achieved by the colloidal filtration process based on the shapes or the sizes of the substances to be separated; by the ion exchange process based on the electric charge of the substances to be separated; and by the affinity chromatographic process based on the specific bonding of the substances to be separated.
For the ion exchange process, the types of the carriers used in the separation process mainly comprise particulate resins, laminated membranes and nanofibrous membranes. The various carriers have different separation properties and requirements. For example, for the particulate resins used in the common packed bed chromatography, the resins must have properties of uniform size, rigidity, high pressure resistance, etc. However, for the column packed with the resins, the possibility of generating a turbulent flow will be decreased if the particulate resins are closely packed, i.e. a space between the particles is reduced. Also, if the particle sizes are reduced, a space of turbulent flow will be reduced and the separation efficiency will be enhanced, even though it may decrease a flow rate of a fluid to be separated.
Further, for the application of the separation or the protein purification, the typical separation or purification process includes a gel chromatography, or membrane separations using an anion or cation-adsorbing membrane, or a nanofibrous membrane having high specificity, wherein the nanofibrous membrane is particularly suitable for the separation or purification process and is attracting a lot of attention due to the properties of high porosity, high specific surface area, low pressure drop, high throughput, etc.
U.S. Pat. No. 5,087,367 discloses a hydrolyzed membrane and a process for the preparation of the same, wherein the membrane is characterized in that the membrane consists essentially of a material which can generate a carboxy group by hydrolysis, such as polyacrylonitrile, and a part of the material is hydrolyzed to have carboxy groups and wherein the said hydrolysis is effected by the alkalization treatment of the membrane using an alkaline solution, such as sodium hydroxide.
U.S. Pat. No. 5,281,337 discloses a membrane system comprising a membrane support layer of a polyacrylonitrile having at least a portion of the surface —CN groups of the support layer hydrolyze to carboxylate salt groups and characterized by a high bonding ability to a membrane separating layer.
US 2004/0241436A1 discloses a nanofiber comprising a polymer and a protein, wherein the polymer and the protein are electrospun to form a protein membrane composition and the protein is covalently bound to the fiber.
Chen et al. disclose a process for the production of the ion-exchange fiber in “The production of ion-exchange fiber by partial hydrolization process of PAN fiber”, Transactions of Beijing Institute of Technology, Vol. 28, No. 2, p. 117-180, 2008. Said process places the PAN fiber under an alkali condition, thereby converting the —CN groups of the microscale PAN fiber to amide groups (—CONH2) and sodium carboxylate groups (—COONa) (i.e. the PAN-COONa type of ion-exchange fiber); followed by acidification in order to obtain the PAN-COOH type of fiber.
Besides, some literatures indicate that the application of ultrasonics in a chemical reaction would enhance the reaction, for example, the literatures published by Yang Yong et al. in “Alkaline Pretreatment of Ethanolized Maize Stalk Enhanced by Ultrasonic Wave”, Journal of Southwest University, Vol. 29, No. 7, 2007 and by Ma et al. in “The research development of the application of the ultrasonic technique in a polymer synthesis”, Polymer materials science and engineering, Vol. 23, No. 5, 2007.
However, there is still a need for separation membranes and separation processes better than the ones disclosed in the above-described patents and references in order to enhance the separation result and lower the production cost of a target product.